1. The Field of the Invention
The present invention relates to catheters used in draining venous blood for treatment in extracorporeal life support equipment during surgical procedures requiring cardiopulmonary bypass. More particularly, the present invention is directed to a venous return catheter adapted for use in draining blood from the right atrium and the vena cavae.
2. The Prior Art
It is a routine requirement of a variety of surgical procedures to utilize extracorporeal cardiopulmonary bypass in order to mechanically perform the functions normally conducted by the heart and lungs. Venous blood depleted in oxygen and rich in carbon dioxide is mechanically removed from the patient and pumped to an oxygenating apparatus in order to oxygenate the blood and remove excess carbon dioxide. The blood is then returned to the patient's arterial system.
It is exceedingly important that adequate volumes of blood be drained from the patient during cardiopulmonary bypass so that the extracorporeal life support equipment can keep up with the patient's need for oxygen and can adequately remove excess carbon dioxide. Insufficient quantities of oxygen can lead to serious tissue damage. Inadequate removal of carbon dioxide leads to a condition known as "acidosis," which can result in serious consequences caused by the alternation in normal metabolic functioning of critical enzymes. Either condition can result in serious injury to the patient.
It will be appreciated that many factors affect the ability to drain adequate volumes of blood from a patient during cardiopulmonary bypass.
Two such factors are the design and placement techniques of drainage catheter used to remove the venous blood from the patient for extracorporeal treatment. Numerous catheter designs and placement techniques have been devised and tested, and various catheter designs and cannulation techniques have been recognized as safe and effective for venous drainage during cardiopulmonary bypass.
One such technique involves placement of a pair of catheters, one into the superior vena cava, and another into the inferior vena cava, in order to collect venous blood returned to the patient's right atrium. This technique is extremely reliable but suffers from the disadvantage that it takes time to surgically place two catheters, and then to suture the insertion locations when the catheters are removed following bypass. Nevertheless, because of problems experienced in connection with conventional single catheter designs discussed below, some physicians continue to utilize a two catheter technique.
A second general technique involves placement of a single catheter. Many physicians prefer a single catheter technique over a two catheter technique because only one incision is required, thereby simplifying and shortening the cannulation procedure both at the time of insertion and at the time of removal. It is also helpful to reduce the number of catheters that a surgeon must work around as he conducts surgery on the patient.
One variation of the single catheter technique involves placement of a catheter so that its distal tip lies in the right atrium. Such a placement permits the catheter to collect blood draining into the right atrium from the inferior vena cava and from the superior vena cava. While this procedure is capable of achieving adequate venous drainage, on occasion the catheter tip is overinserted or otherwise inadvertently manipulated so that the drainage openings in the catheter are pressed against tissue within the right atrium, thereby reducing or even interrupting blood flow into the catheter. This can be extremely dangerous to the patient. Because of these dangers, only a relatively small number of physicians utilize this procedure.
A second variation of the single catheter technique is a hybrid of the two catheter and single catheter techniques described above. Thus, a single catheter is provided having drainage openings not only at the distal end, but also along its length proximal to the distal end. Such a catheter, sometimes referred to as a "dual drainage" catheter, is then inserted through the right atrium and into either the inferior vena cava or the superior vena cava, with the proximal drainage openings positioned within the right atrium. This placement permits blood to be drained simultaneously from the vena cava in which the dual drainage catheter is placed and from the right atrium.
Due to the presence of multple drainage openings along a portion of the length of a dual drainage catheter, blood flow is less likely to become dangerously reduced when utilizing this type of catheter than when utilizing a simple single catheter. However, conventional dual drainage catheter designs still suffer form some significant disadvantages.
Commonly, conventional dual drainage catheters have a multi-diameter structure, with a relatively small diameter distal catheter portion (e.g., 36 French) and a larger diameter proximal portion (e.g., 51 French). Such catheters are typically constructed by forming a molded reducer having elongate slots therein, and then affixing suitable lengths of 36 French and 51 French tubing to opposite sides of the reducer.
Optimally, the distal portion of the catheter is inserted only partially into one of the vena cavae so that the proximal drainage openings remain substantially centered within the right atrium. Sometimes, however, the catheter is overinserted, occasionally so much so that the proximal drainage openings are partially occluded at the entrance to the vena cava, or are actually inserted into the vena cava so that both distal and proximal drainage openings drain from the vena cava, and none drain the right atrium. This results in a substantial reduction in venous drainage.
The conventional dual drainage catheter formed form two lengths of tubing and a molded reducer member also suffers from other disadvantages. For example, the blood flow pathway is interrupted at the two positions where the catheter tubing is connected to the molded reducer. This tends to cause turbulence at these two positions, which in turn can cause damage to red blood cells, and can initiate a clotting reaction.
Yet a further disadvantage when using a reducer and attached tubing is the possibility that one of the tubes will become separated from the reducer during use. Such a separation during bypass could easily result in serious injury to the patient.
Additionally, the use of a molded reducer tends to inflict tissue damage as the reducer is inserted into the right atrium. This is because blood is returned from the patient's venous system to the right atrium under pressure, so that the incision through which the catheter is inserted must be kept tightly closed around the catheter or a significant volume of blood will leak out. As the small diameter leading portion of the catheter is inserted, a clamp is used to hold the heart tissue tightly against the catheter so as to prevent blood leakage. As the catheter continues to be inserted, the reducer eventually comes in contact with the clamped tissue. As noted above, this reducer is unyielding, and has a number of still ridges increasing in diameter from the distal to proximal end that form the drainage openings. As this unyielding reducer is forced through the incision, it is not uncommon to inflict tissue damage. There is also a tendency for tissue to drag or catch on the reducer drainage openings, thereby causing yet additional tissue damage. Even when no damage to tissue results, this tendency of the catheter to "hang up" as it is inserted is a source of irritation to the surgeon and causes him to lose concentration.
Another common difficulty is inherent in the most common dual drainage catheter placement technique. Most often, a dual drainage catheter is used by inserting it through the right atrial appendage and then into the inferior vena cava. Since the inferior vena cava is not directly opposite the right atrial appendage, placement of a catheter using this conventional placement technique results in a bend of about 30 degrees in the distal portion of the catheter.
Normally, this causes no problems. Some surgical procedures, however, require manipulation or movement of the heart. Since the inferior vena cava is substantially anchored in place, manipulation of the heart frequently increases the angle of bend in the portion of the catheter situated at the juncture between the inferior vena cava and the right atrium. Not uncommonly the increased degree of bending causes the catheter to become kinked. This, of course, restricts or even interrupts blood drainage from the inferior vena cava, and hence reduces overall blood drainage.
In veiw of the foregoing it will be appreciated that it would be a substantial contribution in the field of venous return catheters if an improved single venous return catheter could be provided that successfully avoided the aforementioned problems. The present invention provides such an improved catheter.